With rotary processing I get very even development over every square millimeter of the film, and the chances of doing any damage to the film are virtually nil.
Now seriously, why would one brush develop if there are no advantages over rotary processing? In other words, why in the world would you stand there brushing film in the dark when you could just watch it turn around in a drum in the light unless there is some advantage to be had on the final print?
I can understand the logic of those who develp ULF film in trays, but there at least you have the advantag of being able to develop several sheets at a time instead of just one or two as I am able to do with 7X17 and 12X20 film. But the logic of brush develoment escapes me.